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Tech Forum

2020 Issue-3

Electronic Candle Circuit

I’m looking for a simple circuit for a 24 hour electronic candle that uses very little power. The candle would drive a single LED. It would run for x hours (say five), then turn off; 24 hours after it  has first activated, it would automatically turn back on for the predefined time.

I've found several ideas, but most of them surrounded the 555 chip which has a very limited time frame.

Scott Lapp
Simi Valley, CA

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It would be almost trivial to write a small program for a microcontroller to do this. I actually built almost the same thing to turn on a window fan in the evening and off in the morning. An 8 pin PIC with a 32. 768 Khz crystal. A single button reset the processor, which then would time for 24 hours, then activate the fan. Easy enough to add additional times. No display or time setting needed.

Richard Cox
Thousand Oaks, CA

Check out the Custom Silicon Solutions CSS555C Micropower Timer. With a little programming and perhaps a small additional capacitor you will be able to get the delay times your looking for. Also see the article https://www.nutsvolts.com/magazine/article/february2016_CSS555TimerICs

Kurt Stefans
Valparaiso, IN

I built a similar circuit to control a window fan. I wanted it to turn on and off at a certain time each day. I used an 8 pin PIC clocked by a 32.768 KHz crystal. The circuit was installed in the fan's remote controller.

Timer 1 was clocked such that it created a rollover interrupt every second. The software then counted the seconds and incremented a minutes and hour counter. Pressing a button connected to the reset pin set all the counters to zero. Then when the seconds, minutes and hours counters were zero every 24 hours it output a signal to the remote control button to turn the fan on or off.

What you want would turn the candle on when the hours and minutes are zero, then turn it off when the hours are five and the minutes are zero. Contact me at [email protected] for details.

Richard Cox
Thousand Oaks, CA